1. Field of the Invention
The present invention is in the field of lead acid batteries, the structure of the plates for lead acid batteries and methods of manufacturing the same.
2. Related Art
Traditionally, lead acid batteries have included positive plates and negative plates that are immersed in electrolyte and sealed to make the battery. The plates are each made of essentially two elements. The two plate elements include a grid such as that depicted in FIG. 1 which was an electro-conductive material such as lead. This grid comprised an electrode. The plate was completed by embedding this grid in a paste which was a clay-like material in consistency and was electro-conductive. This positive active material (PAM) or negative active material (NAM) filled the spaces between the grid lines or electrodes. These spaces, when filled with paste, were referred to as pellets. Encasing the electrode grid in the paste also established a thin layer of paste on both the top and bottom of the electrodes. When thereafter cured and immersed in electrolyte, the paste created an electroactive pathway between the electrodes and electrolyte. This electroactivity of the paste is high close to the electrodes and diminishes significantly as distance from the electrodes increases. In the traditional, prior art plate structure, the center of the pellet, being farthest from the electrodes, is significantly less electroactive than the cured paste immediately adjacent the electrodes.
FIG. 2a depicts the typical positive plate prior art structure. It shows a cross section of the grid shown in FIG. 1. Electrodes 12 are embedded in paste 14 forming a plate. The plate is then assembled in the battery such that it is surrounded by electrolyte 16. As is best seen in FIG. 2b this structure creates areas of high electroactivity between the electrode 12 and the electrolyte 16, which areas are indicated at 18. However, areas of low electroactivity 20 are also created by the prior art structure. The areas of low electroactivity 20 add weight to the battery without adding power or capacity, and were effectively wasted space in that regard.
This structure had two advantages however. First, it was easy to manufacture. Second, it was robust enough to resist breaking during assembly and cracking during repeated cycles of battery use. Hence, for the sake of structural strength, simplicity and manufacturing expedience, performance suffered.